Whytt and Magendie’s Reflexes

Before Robert Whytt, little was known about human reflexes. Whytt was able to advance our knowledge through a series of experiments; he published the results in 1751. Previous scientists had noticed that decapitated animals (and people) still had muscle twitches. Whytt used decapitated animals to systematically show that he could make their muscles twitch by poking or pinching a leg. Clearly, basic reflexes did not require the brain. Whytt went beyond that though. He was able to dissociate reflex action from the brain by severing nerves between the spinal cord and an appendage. When the connection to the spinal cord was lost, there was no reflex. Whytt’s discoveries about reflexes went beyond simple automatic reflexes. He recognized that there was voluntary and involuntary action. The reflexes that he discovered the spinal cord played a large role in controlling were involuntary. He distinguished between voluntary and involuntary actions and stated that voluntary actions, if practiced enough, become habits. Habits, he stated, became more and more automatic with further practice. So while automatic and voluntary reflexes and actions are distinct they are not mutually exclusive. Whytt’s research was the forerunner to 20th century behaviorism, specifically classical conditioning.

A number of years after Whytt published his work, two independent researchers Sir Charles Bell and Francois Magendie discovered the functions of the two main nerve tracts in and out of the spinal cord. While Bell receives a lot of credit, Magendie’s work was the more scientific and documented – Bell just had a lot of political sway. What did these two researchers discover? Magendie exposed the spinal cord of a live dog and severed the posterior verve tract. The dog could still move its limbs but had no sensation in the affected area. Magendie was then able to sever the anterior root of a nerve tract. He discovered that the animal still had sensation in the affected area but no movement. He put the findings together and stated that the efferent anterior nerves controlled movement while the afferent posterior nerves controlled sensation. Bell had earlier discovered essentially the same thing. The law about the functioning of the nerve pathways became known as the Bell-Magendie law. Neurologists and neuropsychologists have been able to use this law as the basis for understanding different types of central nervous system injury.

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